School Of Basic And Applied Sciences
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Item Janus ?-PdXY (X/Y = S, Se, Te) materials with high anisotropic thermoelectric performance(Royal Society of Chemistry, 2023-02-21T00:00:00) Jakhar, Mukesh; Sharma, Raman; Kumar, AshokTwo-dimensional (2D) materials have garnered considerable attention as emerging thermoelectric (TE) materials owing to their unique density of states (DOS) near the Fermi level. We investigate the TE performance of Janus ?-PdXY (X/Y = S, Se, Te) monolayer materials as a function of carrier concentration and temperature in the mid-range from 300 to 800 K by combining density functional theory (DFT) and semi-classical Boltzmann transport theory. The phonon dispersion spectra and AIMD simulations confirm their thermal and dynamic stability. The transport calculation results reveal the highly anisotropic TE performance of both n and p-type Janus ?-PdXY monolayers. Meanwhile, the coexistence of low phonon group velocity and a converged scattering rate leads to a lower lattice thermal conductivity (Kl) of 0.80 W mK?1, 0.94 W mK?1, and 0.77 W mK?1 along the y-direction for these Janus materials, while the high TE power factor is attributed to the high Seebeck coefficient (S) and electrical conductivity, which are due to the degenerate top valence bands of these Janus monolayers. The combination of lower Kl and a high-power factor at 300 K (800 K) leads to an optimal figure of merit (ZT) of 0.68 (2.21), 0.86 (4.09) and 0.68 (3.63) for p-type Janus PdSSe, PdSeTe and PdSTe monolayers, respectively. To evaluate rational electron transport properties, the effects of acoustic phonon scattering (?ac), impurity scattering (?imp), and polarized phonon scattering (?polar) are included in the temperature-dependent electron relaxation time. These findings indicated that the Janus ?-PdXY monolayers are promising candidates for TE conversion devices. � 2023 The Royal Society of Chemistry.Item Janus ?-Te2X (X = S, Se) monolayers for efficient excitonic solar cells and photocatalytic water splitting(Royal Society of Chemistry, 2023-01-04T00:00:00) Singh, Jaspreet; Kumar, AshokHighly efficient, environmentally friendly and renewable sources of energy are of great need today to combat increasing energy demands and environmental pollution. In this work, we have investigated the novel 2D allotropes, i.e., ?-Te2X (X = S, Se), using first-principles calculations and study their potential applications in light harvesting devices. Both the monolayers possess high stability and semiconducting nature with an indirect band gap. The high carrier mobilities and excellent optical absorption of these monolayers make them potential candidates for solar conversion applications. We have proposed the type-II heterojunction solar cells and calculated their power conversion efficiencies (PCEs). The small conduction band offset and appropriate band gap of donor material in the case of ?-Te2S(S-Side)/?-Te2S(Te-Side) heterojunction results in a PCE of ?21%. In addition, the band alignments of these monolayers properly engulf the redox potentials of water. The overpotentials required to trigger hydrogen reduction (HER) and water oxidation (OER) half reactions reveal that HER and OER preferred acidic and neutral media, respectively. The calculated solar-to-hydrogen (STH) efficiencies of ?-Te2S (?-Te2Se) monolayers turn out to be ?13% (?12%), respectively, which implies their practical applications in water splitting. Thus, our work provides strong evidence regarding the potential applications of these materials in the field of light harvesting devices. � 2023 The Royal Society of Chemistry.Item Photocatalytic properties of anisotropic ?-PtX2 (X = S, Se) and Janus ?-PtSSe monolayers(Royal Society of Chemistry, 2022-09-01T00:00:00) Jamdagni, Pooja; Kumar, Ashok; Srivastava, Sunita; Pandey, Ravindra; Tankeshwar, K.The highly efficient photocatalytic water splitting process to produce clean energy requires novel semiconductor materials to achieve a high solar-to-hydrogen energy conversion efficiency. Herein, the photocatalytic properties of anisotropic ?-PtX2 (X = S, Se) and Janus ?-PtSSe monolayers were investigated based on the density functional theory. The small cleavage energy for ?-PtS2 (0.44 J m?2) and ?-PtSe2 (0.40 J m?2) endorses the possibility of mechanical exfoliation from their respective layered bulk materials. The calculated results revealed that the ?-PtX2 monolayers have an appropriate bandgap (?1.8-2.6 eV) enclosing the water redox potential, light absorption coefficient (?104 cm?1), and exciton binding energy (?0.5-0.7 eV), which facilitates excellent visible-light-driven photocatalytic performance. Remarkably, the inherent structural anisotropy leads to an anisotropic high carrier mobility (up to ?5 � 103 cm2 V?1 S?1), leading to a fast transport of photogenerated carriers. Notably, the required small external potential to realize hydrogen evolution reaction and oxygen evolution reaction processes with an excellent solar-to-hydrogen energy conversion efficiency for ?-PtSe2 (?16%) and ?-PtSSe (?18%) makes them promising candidates for solar water splitting applications. � 2022 The Royal Society of Chemistry.Item Mechanical, optical and thermoelectric properties of Janus BiTeCl monolayer(Elsevier Ltd, 2022-04-29T00:00:00) Chauhan, Poonam; Singh, Jaspreet; Kumar, AshokWe report mechanical, optical and thermoelectric properties of recently fabricated Janus BiTeCl monolayer using density functional and semi-classical Boltzmann transport theory. Janus BiTeCl monolayer exhibits a direct bandgap, high carrier mobility (?103 cm2V?1s?1) and high optical absorption in the UV�visible region. The mechanical behavior of the Janus BiTeCl monolayer is nearly isotropic having an ideal tensile strength ?15 GPa. The higher value of the Gruneisen parameter (?), a low value of phonon group velocity (vg), and very little phonon scattering time (?p) lead to low lattice thermal conductivity (1.46 W/mK) of Janus BiTeCl monolayer. The combined effect of thermal conductivity and electronic transport coefficients of Janus BiTeCl monolayer results in the figure of merit (ZT) in the range of 0.43�0.75 at 300�500 K. Our results suggest Janus BiTeCl monolayer be a potential candidate for optoelectronic and moderate temperature thermoelectric applications. � 2022Item Two-dimensional ?-PdX2 (X = S, Te) monolayers for efficient solar energy conversion applications(Royal Society of Chemistry, 2022-02-09T00:00:00) Jakhar, Mukesh; Kumar, AshokThe search for highly effective and environmentally safe photocatalysts for water splitting and photovoltaic solar cells is essential for renewable solar energy conversion and storage. Based on first-principle calculations, we show that novel 2D ?-PdX2 (X = S, Te) monolayer possesses excellent stability and great potential in solar energy conversion applications. Comprehensive studies show that the ?-PdS2 monolayer exhibits semiconductor characteristics with an indirect gap, suitable band alignment, efficient carrier separation, and high solar to hydrogen (STH) efficiency, supporting its good photoelectronic performance. The surface catalytic and adsorption/intercalation energy calculation reveals that the photogenerated electrons have adequate driving forces to render hydrogen reduction half-reactions to proceed spontaneously and the ability to cover and incorporate water molecules on the ?-PdS2 monolayer. Besides, the ?-PdTe2 monolayer is a promising donor material for excitonic solar cells with high photovoltaic performance. More importantly, due to suitable donor band gap and small conduction band offset in the proposed type-II heterostructure, the power conversion efficiencies (PCE) were calculated up to ?23% (?-PdTe2/WTe2), ?21% (?-PdTe2/MoTe2) and ?18% (?-PdTe2/?-PdS2), making it a promising candidate for solar energy conversion applications. � 2022 The Royal Society of ChemistryItem Tunable photocatalytic water splitting and solar-to-hydrogen efficiency in ?-PdSe2monolayer(Royal Society of Chemistry, 2021-08-18T00:00:00) Jakhar, Mukesh; Kumar, AshokDirect production of hydrogen from photocatalytic water splitting is a potential solution to overcome global energy crisis. Herein, based on first-principles calculations, we demonstrate that the two-dimensional ?-PdSe2 monolayer is a promising candidate for efficient photocatalytic water splitting in acidic and alkaline media as well as neutral medium with highly efficient solar-to-hydrogen efficiency. ?-PdSe2 monolayer shows low cleavage energy which endorses the possibility of its mechanical exfoliation from layered bulk ?-PdSe2. Remarkably, ?-PdSe2 monolayer is semiconducting with indirect band gap of 1.96 eV with perfect engulfing the redox potential of water in a wide range of pH of medium. ?-PdSe2 monolayer exhibits good light harvesting ability and adequate driving forces for water redox reaction in wide range of pH (0 to 12). Comprehensive investigation of pH dependent water splitting indicates that the ?-PdSe2 monolayer is a better candidate for efficient water splitting in alkaline media rather than acidic or neutral medium. In addition, high solar-to-hydrogen efficiency as high as ?17% is obtained that shows ?-PdSe2 monolayer a promising candidate for overall photocatalytic water-splitting. � The Royal Society of Chemistry.